Wood preservative composition

ABSTRACT

A wood preservative composition having improved penetration properties comprises 15-90% by volume of coal-tar creosote, up to 45% by volume of coal tar, 7-66.5% by volume of paraffinic wax and 0.5-21% by volume of a high boiling paraffinic oil (i.e. an essentially hydrocarbon oil no more than 5% of which boils below 315 DEG C. at 1 atm. pressure), the volumetric ratio of creosote to coal tar being at least 1:1 and of wax to oil 2.3:1 to 19:1.  The paraffinic wax may have a m.pt. of 35 DEG -58 DEG C. and the wax and/or oil may have an average M.W. of 280-340.  The oil preferably contains at least 80% by volume of paraffinic hydrocarbons.  10 to 85% by volume of the paraffinic wax and oil content of the composition may be constituted by a soft wax product obtained by solvent de-oiling of crude wax obtained by solvent dewaxing of high viscosity index distillate lubricating oil.

United States Patent Ofitice 3,278,377 Patented Oct. 11, 1966 3,278,377WGOD PRESERVATHVE COMPOSITION Anthony P. Ferrucci, Jr., Villa Park, Ill,assignor to Shell Oil Company, New York, N.Y., a corporation of DelawareN Drawing. Filed Mar. 12, 1964, Ser. No. 351,527 2 Claims. (Cl.167-38.6)

This invention relates to wax-containing compositions. Moreparticularly, the invention relates to Waxand oilcontaining compositionswhich are very useful for the treating and preservation of wood.

All wood of any commercial importance is subject to deterioration aftercutting, and the degree and kind of deterioration depends on the type ofuse to which the wood is put. There are, of course, a number of naturalagencies of wood deterioration, among which are wood-destroying(decay-producing) fungi, wood-staining fungi, molds, wood-boring insectssuch as termites, powder-post beetles and carpenter ants, marine borerssuch as ship worms, martesia, limnoria, sphaeroma and chelura, and thedifferent kinds of deterioration which are normally referred to asweathering.

Among the most effective and economical materials known for general usein the protection of wood against all forms of wood-destroying agenciesare coal-tar creosote and mixtures of coal tar and coal-tar creosote.Coaltar creosote is produced by distillation of coal tar which consistsof the condensable liquids made by carbonization of bituminous coal atelevated temperatures. It is comprised principally of liquid and solidaromatic hydrocarbons and contains appreciable quantities of tar acids(e.g., pyridines, quinolines, acridines) and tar bases (e.g., phenols,cresols). Creosote usual-1y has a boiling range Width of at least 125C,the initial boiling point being in the range of ISO-200C, the finalboiling point being in the range 300450C. The higher boiling portions ofcreosote may contain appreciable amounts of fluorene, anthracene andphenanthrene.

Creosote-coal tar solutions are frequently used in place of creosotealone primarily to reduce the preservative cost. Such solutions may beeither a solution of coal tar in distillate oil (creosote) or aso-called coal-tar distillate oil. They are comprised of at least 50%coal tar and should contain no more than 3 by volume water and no morethan 24% weight benzene insolubles, this amount being directly relatedto the amount of coal tar in the solution.

There are, of course, many other closely related wood preservatives.Among these is water-gas tar and watergas tar creosote which is producedby distillation of water-gas tar, a by-product in the manufacture ofwatergas from petroleum oils. Water-gas tar and water-gas tar creosoteare not, however, considered to be as effective as coal-tar creosote.Wood-tar creosote, produced by distillation of wood tar, is an effectivewood preservative. However, it is more expensive than coal-tar creosoteand not quite as effective as coal-tar creosote. Petroleum oils haveoccasionally been tried as wood preservatives; however, they possessvery low toxic properties when used alone. Consequently, their use hasbeen limited to diluents for other preservative oils such as coal-tarcreosote and solvents for toxic chemicals such as pentachlorophenol.

Coal tar and coal-tar creosote (hereinafter referred to as creosote)preservatives are applied to wood by a wide variety of processes. Forexample, non-pressure processes are used as brushing, spraying, dipping,steeping and cold soaking. The most widely used processes for treatingwood with preservatives are those which are conducted under pressure. Insuch pressure processes,

the wood is impregnated in a closed vessel with the preservative,usually in the liquid form, at pressures up to, say, 250 psi. andtemperatures on the order of 180- 220F. By using such pressureprocesses, the degree of penetration of the preservative into the woodis maximized as well as retention of the treating agent. There are manyvariants to the pressure process; for example, the wood may first besubjected to a vacuum before pressure impregnation to exhaust air fromthe wood. On the other hand, in other treating processes air isdeliberately forced into the wood prior to impregnation in order tofacilitate removal of excess preservative and to reduce bleeding anddripping of the preservative upon the completion of the treatment.

In any of these processes, however, it is desired to obtain (1) completeand thorough penetration of the wood preservative with the wood,

(2) adequate retention of the preservative within the wood, and

(3) minimum amounts of bleeding of the preservative from the wood uponsubsequent exposure to outdoor weather conditions.

In the treatment of wood with preservatives, it is important thatretention of the preservative in the wood be high in order to provide areserve against depletion by leaching and evaporation. By retention ismeant the net amount of treating solution which is retained in the woodafter impregnation. Retention is usually measured at the time oftreatment by determination of the consumption of treating solution,allowing, of course, for any other known non-retentive losses. Theminimum amount of retention depends on many factors-the type of wood,the type of service to which the wood is to be put, and the kind ofpreservative used. Illustrative of the required minimum retention,however, is 5-10 pounds per cubic foot which is specified by therailroads for impregnation of railroad ties with coal-tarcreosote-containing compositions.

Equally important is the degree of penetration of the preservative intothe wood. Obviously, in order to assure more nearly complete protectionof the wood, penetration of the preservative should be complete (100%).With most preservatives, including coal-tar creosote, however,penetration is less than complete and minimum values are specified,depending on the preservative and the properties of the wood. Thoughwith some woods it is impossible to obtain complete penetration, it isnevertheless desirable to obtain the highest possible degree ofpenetration.

Penetration is usually measured by making incremental borings or hitholes in the wood a sufiicient distance from the end of the treatedpiece of wood to escape the effect of end penetration. Such borings areobserved as to penetration promptly after boring. In the case of darkcolored preservatives, the degree of penetration is determined by visualobservation of the depth of color change in the wood. When oils are usedwhich do not perceptively change the color of the wood, reagents areused to induce color-producing reactions with the oil, therebyfacilitating visual observation of the penetration of the preservative.

Applicant has now discovered a unique coal-tar creosote-containingwood-preservative composition which retains the desirable preservativeproperties of coal-tar creosote while having greatly improvedpenetration properties. More specifically, applicants wood-preservativecomposition consists essentially of 15 to by volume normally liquidcreosote, 0 to 45% by volume normally liquid coal tar, the volumetricratio of creosote to coal tar being at least 1.0:1, 7 to 66.5% by volumeWax and 0.5 to 21.0% by volume of a high-boiling paraffinic petroleumoil, the volumetric ratio of wax-to-oil being from about 2.3:1 to about19: 1. Within the foregoing limits, it is preferred that the volumetricratio of creosote to coal tar be at least about 1.5 :1 and thevolumetric ratio of wax to oil from about 4:1 to about 9:1.

As the wax component of the preservative composition, it is preferred touse a low-melting-point petroleum paraffinic distillate wax such as thatobtained from the dewaxing of petroleum lubricating oil stocks. By lowmelting point is meant an ASTM D87 wax melting point of less than 135 F.and preferably no greater than 120 F. The minimum melting point willnot, however, be lower than 95 F. In some instances where the amount ofoil in the wax is high, the wax or the wax-oil mixture which is used inthe invention may not have a distinct melting point, in which case itspoint of phase change is measured by the ASTM D938 Congeal Point. Suchoily waxes and wax-oil mixtures have been found to be particularlysuitable in the composition of the invention. It is preferred that thewax contain no substantial amounts of microcrystalline or amorphous wax,which is normally present in all except certain specially refinedresidual waxes. It is also preferred that the preservative compositioncontain at least 10% by volume wax and, still more preferably, at leastby volume wax.

As the oil component of the composition of the invention, it ispreferred to employ a high-boiling paraflinic petroleum oil, preferablyone containing at least 80% paratfinic hydrocarbons and less thanaromatic hydrocarbons. High-boiling oils containing at least 90%parafiinic hydrocarbons are preferred, especially those oils theparaffins in which contain a high degree of side-chain branching. By theterm high-boiling oil is meant an essentially hydrocarbon oil no morethan about 5% of which boils below 600 F. when heated at one atmospherepressure. Thus it is intended to include within this definition oilsWithin the boiling and viscosity range of distillate lubricating oilswhich, of course, are substantially vaporizable at 600 F. only at belowatmospheric pressures. The above-described oils, which are useful in thecompositions of the invention may be derived from parafiinic, naphthenicor mixed-base crudes. Thus, they frequently will contain 1530% ofnaphthenic (cycloparaffinic) components. Within the above-mentionedlimits regarding paraffins and aromatics, however, the amount ofnaphthenes is not especially important. The relatively non-polarcharacteristics of petroleum lubricating oils are, however, greatly tobe desired.

It is preferred that both the oil and wax be of comparatively lowaverage molecular weight, i.e., from 280 to no more than 420 and stillmore preferably no more than about 340.

Both the wax and the oil may be fully or only partially refined. Theymay also be obtained from either the same or different crude oilfractions. Not infrequently, it is possible to obtain the wax and oil inthe correct proportions from the same fraction. For example, the softwax product obtained by solvent de-oiling of crude wax obtained bysolvent dewaxing of high-viscosity-index distillate lubricating oils isparticularly suitable without further adjustment of composition. Inaddition, certain crude or slack waxes obtained by dewaxing distillatelubricating oils are likewise frequently suitable. More rarely, certainundewaxed distillate lubricating oil stocks containing very high amountsof wax can also be used. Conversely, highly refined waxes and oils canlikewise be employed. The customary refining treatments of such Waxesand oils, e.g., hydrotreating, acid treating, percolation, etc. have noadverse effect on their efiicacy in the compositions of the invention.

The compositions and their unique character will better be understood byreference to the following examples:

Example I Four charges of wooden railroad crossties, each containingover 500 ties, were treated with Wood preservative in a commercial scalepressure-treating facility. Two of the charges were treated with aconventional woodpreservative composition consisting of 60% creosote and40% coal tar. The remaining two charges were treated under the sameoperating conditions with a waxand oilcontaining wood-preservativecomposition in accordance with the invention. The waxand oil-containingpreservative consisted of by volume of 60/40 creosote-coal tar mixtureand 15 by volume of soft wax byproduct produced from the solventdewaxing of a H.V.I. distillate lubricating stock oil. The soft waxcontained about 29% by volume oil. The over-all composition of thewaxand oil-containing preservative was therefore as follows:

Creosote percent v. 51.0 Coal tar do 34.0 Wax do 10.7 Oil do 4.3Creosote-coal tar ratio volume 1521 Wax-oil ratio do 2.5:1

All four charges of crossties were treated to refusal, i.e., until nomore preservative was taken up by the Wood. The treating temperature wasl85200 F. The results are tabulated in the following table:

Table L-Commereial Scale Treatment of Railroad Crossties withConventional Prescrvative versus Wax-Oil-Containing PreservativePreservative Composition- Creosote 60 60 51 51 Goal Tar 40 4O 34 34 Wax10. 7 10. 7 Oil 4. 3 4. 3 Preservative Properties:

Specific Gravity at 60 F 1. 106 1.106 1.068 1.068 Viscosity, SSU at- F42. 2 42. 2 46. 6 46. 6 F 30. 0 36.0 40. 0 40. 0 210 F 34. 3 34. 3 34. 234. 2 Pour Point, F +5 +5 +80 +80 Number of Crossties e 556 551 509 567Species:

Red Oak, percent 86 83 80 83 White Oak, percent. 17 20 17 Retention,lbs./lt. 8. 45 7. 92 9. 04 Penetration, percent b White Oak 1O 20 20 RedOak 30-50 100 100 5 Dimensions of all crossties 7 x 9 x 8. Penetrationdetermined by 5 long borings taken through 9" dimension.

The results of the foregoing test are quite striking because of thecomplete penetration obtained with the wax-oil-creosote composition ascompared with the mere 30-50% penetration obtained with the conventionalcreosote-coal tar preservative composition. The results were especiallynoteworthy in that complete penetration was obtained on the crosstiesmade of white oak which is classified by the US. Dept. of AgricultureForest Service in Agriculture Handbook No. 40 as being Heart wood verydifficult to penetrate. It is also noteworthy that greater penetrationwas obtained with the wax-oilcreosote composition despite the fact thatthe viscosities of the two compositions were almost identical. Theforegoing data also indicate that the compositions of the invention areof significant economic advantage in that at least twice as muchpenetration of the Wood (ergo protection of the wood) was obtained withonly 3.57% more treating solution.

Example 11 Two charges of railroad crossties containing an equal numberof crossties made from Engelmann spruce were treated separately at thesame operating conditions. One charge was treated with a standardsolution of pentachlorophenol in petroleum oil, the other was treatedwith the creosote-Wax-oil composition of Example I. Upon examination ofthe treated crossties it was found that the pentachlorophenol-oilsolution had penetrated an average of only inch, whereas thecreosote-Wax-oil composition had penetrated an average of greater than/2 inch. The Engelmann spruce ties used in this test were ofparticularly close grain and dense cell structure, hence the lowpenetrations. Ordinarily, suchwood would not be usable for crosstiesbecause of the virtual impossibility of treating it adequately withexisting preservatives and processing means. However, the eight timesgreater penetration obtained with the composition of the invention, eventhough only /2 inch, is sufficient to give adequate preservative action.Thus, in effect, some woods, heretofore unusable, can be upgraded ineconomic value by the superior penetration capability of thewax-creosote-oil composition of the invention.

In the foregoing examples, the properties of the oil, wax and oil-waxmixture were as follows:

TABLE IL-PROPERTIES OF OIL WAX AND OIL-WAX MIXTURE Wax Oil Oily WaxViscosity, SSU at 210 F 35. 3 37. 8 36. 1 Average Molecular Weight 322322 322 Melting Point (D87), F 112 Congeal Point (D939), F 105 It is tobe noted that the characterization of hydrocarbons as oil or as waxdepends in part upon the meth- 0d by which they are produced. That is,in the dewaxing of oils or the deoiling of waxes, whether or not aparticular fraction is contained in the wax fraction or in the oilfraction depends upon the process conditions by which they areseparated. In order to have a datum plane for this purpose, thefollowing standardized deoiling procedure is used to characterize theoils and waxes referred to herein:

The hydrocarbon material is dissolved in a 60/ 40 (by volume) mixture ofmethyl ethyl ketone and toluene and cooled to 0 F. The cooled materialis then filtered. The resultant filter cake is redissolved in warm freshsolvent and recrystallized by cooling again to 0 F. and filtered. Therecrystallized cake is washed with additional solvent and repulped butnot redissolved by mixing the washed cake with cold (0 F.) solvent andfiltered to remove the solvent. Additional cold solvent is finally usedto wash the repulped and filtered wax, and the wax is washed. Each ofthe oil fractions is then recombined, either before or after solventremoval if the properties and weight of the oil are to be determined.The solvent to feed volumetric ratios employed are as follows:

Repulping Wash 1: 1

I claim as my invention:

1. A wood preservative composition comprising (a) at least about 51% byvolume of coal tar creosote, (b) at least about 34% by volume of coaltar, (c) at least about 10% to 66.5% by volume of low melting pointparafiinic wax obtained by solvent deoiling of crude wax obtained bysolvent dewaxing of high viscosity index petroleum distillatelubricating oil stocks, said wax being further characterized as havingno substantial amounts of microcrystalline or amorphous wax, an ASTM D87wax melting point of between about F. and F. and an average molecularweight of from 280 to no more than 420; (d) at least about 3.621% byvolume of high-boiling paraflinic oil containing at least 80% by volumeof parafiinic hydrocarbons and no more than 20% by volume aromatichydrocarbons, said oil being further characterized as having no morethan about 5% of an essentially hydrocarbon oil which boils below 600 F.when heated at one atmosphere pressure, an average molecular Weight offrom about 280 to about 340, and

the relatively non-polar characteristics and viscosity range ofpetroleum distillate lubricating oils derived from paraffinic,naphthenic, or mixed-base crudes.

2. In the art of impregnation of wood and improvement which consistsessentially of the step of impregnating wood with the composition ofclaim 1 thereby to obtain an improved degree of penetration of saidwood.

References Cited by the Examiner UNITED STATES PATENTS 1,041,604 10/1912Dehnst 117-149 1,556,570 10/1925 Coolidge 117-116 1,648,294 11/1927Coolidge 117-149 1,648,295 11/ 1927 Coolidge 117-92 1,976,221 10/1934Goodwin et a1 167-387 2,078,570 4/1937 Holmes 167-387 2,296,401 9/1942Perkins 16738.7 2,310,194 2/ 1943 Harvey 196-50 2,892,261 6/1959Hutchinson 34-95 2,907,684 10/1959 Partansky 117-149 3,061,508 10/1962Morriss et a1. 167-42 OTHER REFERENCES Chem. Abstracts 20: 3550 (2),3551 (4), (1926). Chem. Abstracts 30: 8558 (7), 8560(8), (1936). Chem.Abstracts 57: 1130c (1962).

LEWIS GOTTS, Primary Examiner.

ELBERT L. ROBERTS, Examiner.

S. K. ROSE, Assistant Examiner.

1. A WOOD PRESERVATIVE COMPOSITION COMPRISING (A) AT LEAST ABOUT 51% BYVOLUME OF COAL TAR CREOSOTE, (B) AT LEAST ABOUT 34% BY VOLUME OF COALTAR, (C) AT LEAST ABOUT 10% TO 66.5% BY VOLUME OF LOW MELTING POINTPARAFFINIC WAX OBTAINED BY SOLVENT DEOILING OF CRUDE WAX OBTAINED BYSOLVENT DEWAXING OF HIGH VISCOSITY INDEX PETROLEUM DISTILLATELUBRICATING OIL STOCKS, SAID WAX BEING FURTHER CHARACTERIZED AS HAVINGNO SUBSTANTIAL AMOUNTS OF MICROCRYSTALLINE OR AMORPHOUS WAX, AN ASTM D87WAX MELTING POINT OF BETWEEN ABOUT 95*F. AND 135*F. AND AN AVERAGEMOLECULAR WEIGHT OF FROM 280 TO NO MORE THAN 420; (D) AT LEAST ABOUT3.6-21% BY VOLUME OF HIGH-BOILING PARAFFINIC OIL CONTAINING AT LEAST 80%BY VOLUME OF PARAFFINIC HYDROCARBONS AND NO MORE THAN 20% BY VOLUMEAROMATIC HYDROCARBONS, SAID OIL BEING FURTHER CHARACTERIZED AS HAVING NOMORE THAN ABOUT 5% OF AN ESSENTIALLY HYDROCARBON OIL WHICH BOILS BELOW600* F. WHEN HEATED AT ONE ATMOSPHERE PRESSURE, AN AVERAGE MOLECULARWEIGHT OF FROM ABOUT 280 TO ABOUT 340, AND THE RELATIVELY NON-POLARCHARACTERISTICS AND VISCOSITY RANGE OF PETROLEUM DISTILLATE LUBRICATINGOILS DERIVED FROM PARAFFINIC, NAPHTHENIC, OR MIXED-BASE CRUDES.